The organic light emitting diode (OLED) display is one of the hotspots in the current research field of panel display. Compared with the liquid crystal display, the OLED display has the advantages of low power consumption, low production cost, self-luminous, wide visual angle and high response speed. At present, in the panel display field such as mobile phone, PDA, digital camera, the OLED display has begun to replace the conventional liquid crystal display (LCD). The pixel circuit design is the core technical content of the OLED display and has important research significance.
Different from the LCD that uses voltage to control the brightness, the OLED belongs to current driving, which needs to be controlled to emit light using current. For example, the existing 2T1C pixel circuit, as shown in FIG. 1, the circuit comprises a drive transistor T2, a switch transistor T1, a storage capacitance Cs and an OLED. The switch transistor T1 plays the function of a switch, the drive transistor T2 plays the function of controlling the current flowing through the OLED. When the OLED emits light, from the saturation current formula of the drive transistor T2: I=K(VGS−Vth)2=K(VData−VDD−Vth)2 it can be seen that the current of the drive transistor T2 is determined by the difference value between the voltage VData of the data signal Data and the voltage VDD of the DC voltage signal VDD. The DC voltage signal VDD is a constant signal, hence, the main factor that determines the current of the drive transistor T2 is the voltage VData of the data signal Data.
However, with the continuous increase of the current efficiency of the OLED, the current that needs to be supplied by the drive transistor T2 for the same brightness becomes smaller and smaller. This causes the range of the required voltage VData of the data signal Data smaller and smaller in order to realize 256 gray scale display, particularly the voltage required for realizing the minimum gray scale will become very small, thereby making it very difficult for the drive IC to provide such a small voltage value accurately.